CloudSat is a NASA Earth observation satellite, which was launched on a Delta II rocket on 28 April 2006. It uses radar to measure the altitude and properties of clouds, adding to information on the relationship between clouds and climate in order to help resolve questions about global warming. CloudSat will fly in formation in the '', with several other satellites (Aqua, Aura, CALIPSO and the French PARASOL).

The mission was selected under NASA's Earth System Science Pathfinder program in 1999. The main instrument on CloudSat is the Cloud Profiling Radar (CPR), a 94-GHz nadir-looking radar that measures the power backscattered by clouds as a function of distance from the radar. The CPR was developed jointly by NASA and the Canadian Space Agency. The overall design of the CPR is simple, well understood, and has a strong heritage from the many cloud radars already in operation in ground-based and airborne applications. Most of the design parameters and subsystem configurations are nearly identical to those for the Airborne Cloud Radar, which has been flying on the NASA DC-8 aircraft since 1998.

CloudSat's primary mission is scheduled to continue for twenty-two months in order to allow more than one seasonal cycle to be observed. Based on radar lifetime data, NASA expects the radar is expected to operate for three years with a 99 % probability.

The CPR capitalizes on existing radar expertise and experience at the Jet Propulsion Laboratory. Other radars already flown successfully or being developed by JPL include the Seasat SAR, SIR-A, SIR-B, SIR-C, the Shuttle Radar Topography Mission, Cassini Radar, NSCAT, QuickScat, and SeaWinds.